The snubbing element of the invention is typically used during hydraulic workover operations in gas wells having downhole pressures ranging up to about 3,200 psi or greater. The apparatus can also be used as a pipe wiper in high pressure wells in conjunction with conventional snubbing apparatus utilizing spaced apart blowout preventers. Historically, workover operations in a pressurized well were only performed after pumping heavy drilling mud into the well to force the gas back into the formation, thereby alleviating the borehole pressure. However, this procedure can kill or damage the well, particularly in delicate formations, thereby preventing or severely reducing subsequent production. As a solution to this problem, snubbing elements were developed which permit such wells to be worked under pressure without fear of killing production or of releasing explosive gases into the atmosphere.
Conventional snubbing elements typically comprise a precast, nonsparking metallic support member, usually made of brass or bronze, onto which a polymeric sealing member is molded. The metallic support member comprises a toroidal outer ring that defines the major diameter of the snubbing element, and an inwardly extending web portion that defines a centrally disposed axial bore. The web portion is further provided with a plurality of circumferentially spaced ports and/or lugs to assist in forming a mechanical interlock between the metallic support member and the polymeric sealing member. The polymeric sealing member is typically formed by molding a flowable polymeric resin such as polyurethane around the metallic support member according to conventional molding techniques. When the snubbing element is removed from the mold, the relatively smooth, outwardly facing surface of the toroidal ring is the only portion of the metallic support member which is not embedded in the polymeric material.
During use, the conventional snubbing element is desirably installed inside a steel bowl disposed beneath the blowout preventers at the wellhead. The sealing member of the snubbing element fills the annulus around the tubing and provides sealing engagement with the tubing as it is run into and out of the hole. The metallic outer ring at the top of the snubbing element is used for clamping the snubbing element in its proper alignment inside the bowl. Representative conventional snubbing elements are commercially available from Supreme Rubber Products Co., of Houston, Tex. and from The Altair Co. of Richardson, Tex.
The use of a metallic member was heretofore believed necessary to obtain the desirable degree of strength and resistance to pressure. Moreover, numerous difficulties have been encountered in manufacturing the conventional snubbing elements, and the separately cast nonsparking metallic support member significantly increases the cost of the parts.